Chemistry - 9202 OxfordAQA

Preparation Of Salts

Visão Geral

Somewhere in the building you are sitting in there is almost certainly a bag of plaster, a tub of Epsom salts, a fertiliser sack or a packet of baking powder. Every one of them is a salt, and every one of them was made on purpose by a chemist who first had to answer a deceptively small question: does the thing I am trying to make dissolve in water or not? That single answer decides everything else. It chooses the starting materials, it chooses the apparatus, and it decides whether the product arrives as crystals grown slowly from a warm liquid or as a cloudy solid that appears in a fraction of a second the instant two clear solutions meet.

This lesson gives you the whole decision tree and then walks each branch of it in detail. You will learn the solubility rules that let you sort any salt into soluble or insoluble before you touch a single bottle, the three acid-based routes to a soluble salt and why a route that works beautifully for copper would be dangerous for sodium, the reason chemists deliberately add too much of one reactant and then throw the leftovers away, and the patient technique that turns a colourless solution into a dish of grown crystals. By the end you will be able to plan a preparation for a salt you have never made, which is precisely what the examiner asks you to do.

Objetivos

  1. Soluble salts can be made from acids by reacting them with: metals - not all metals are suitable; some are too reactive and others are not reactive enough; insoluble bases - the base is added to the acid until no more will react and the excess solid is filtered off; alkalis - an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution. Students should be able to suggest methods to make a named soluble salt.
  2. Salt solutions can be crystallised to produce solid salts.
  3. Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed. Precipitation can be used to remove unwanted ions from solutions: for example, in treating water for drinking or in treating effluent. Students should be able to name the substances needed to make a named insoluble salt.

Mapa mental

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Nota de Aula

A salt is what remains when the hydrogen of an acid has been handed over to a metal, or to the ammonium group, and something else has carried the hydrogen away. Sodium chloride is a salt. So are the calcium sulfate in a plaster cast, the ammonium nitrate spread on a field, the copper(II) sulfate that stains a school beaker blue, and the barium sulfate a patient swallows before an abdominal scan. The name of any one of them is assembled from two parts, and both parts are chosen for you by your starting materials: the metal at the front comes from whatever you neutralise the acid with, and the family name at the back comes from the acid itself.

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Avaliação da Lição

Parabéns por concluir a lição em Preparation Of Salts. Agora que você explorou o conceitos e ideias-chave, é hora de colocar seu conhecimento à prova. Esta seção oferece uma variedade de práticas perguntas destinadas a reforçar sua compreensão e ajudá-lo a avaliar sua compreensão do material.

Irá encontrar uma mistura de tipos de perguntas, incluindo perguntas de escolha múltipla, perguntas de resposta curta e perguntas de redação. Cada pergunta é cuidadosamente elaborada para avaliar diferentes aspetos do seu conhecimento e competências de pensamento crítico.

Use esta secção de avaliação como uma oportunidade para reforçar a tua compreensão do tema e identificar quaisquer áreas onde possas precisar de estudo adicional. Não te deixes desencorajar pelos desafios que encontrares; em vez disso, vê-os como oportunidades de crescimento e melhoria.

  1. Which salt is produced when copper(II) oxide reacts with dilute nitric acid? A. copper(II) nitrate B. copper(II) sulfate C. copper(II) chloride D. copper(II) carbonate Answer: A
  2. Which of these salts is insoluble in water? A. sodium carbonate B. potassium sulfate C. barium sulfate D. zinc nitrate Answer: C
  3. A student adds excess magnesium oxide to warm dilute hydrochloric acid, then filters the mixture. What is present in the filtrate? A. magnesium oxide only B. magnesium chloride solution C. hydrochloric acid only D. solid magnesium chloride Answer: B
  4. Which pair of solutions would produce a precipitate of silver chloride? A. silver nitrate and sodium nitrate B. sodium chloride and potassium nitrate C. silver nitrate and sodium chloride D. silver chloride and sodium nitrate Answer: C
  5. Why is a titration used to prepare potassium nitrate rather than adding excess potassium hydroxide to nitric acid and filtering? A. Potassium nitrate is insoluble in water. B. Potassium hydroxide dissolves, so an excess of it cannot be filtered off. C. Nitric acid does not react with potassium hydroxide. D. The reaction produces a gas that must be measured. Answer: B

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